Some memory systems such as SSDs (solid state drive) or memory cards include a plurality of NAND-type flash memory devices in which an erasing process is necessary before a writing process is performed. In a process of writing and erasing data to and from the NAND-type flash memory device, electrons are injected to and discharged from a floating gate by applying a high voltage between a substrate and a control gate. If the data writing and erasing process is performed many times to write and erase data in and from the NAND-type flash memory device, a gate insulation film near the floating gate may deteriorate. Thus, the reliability of the NAND-type flash memory device (non-volatile memory device) tends to deteriorate.